Where is the thermostat on a 1990 G30 Chevy van?

The thermostat on a 1990 Chevy G30 van is located on the engine, under the intake manifold. It's not easily accessible and requires removing components to reach it. You'll likely need to consult a repair manual specific to your van's engine (e.g., a 4.3L V6, 5.7L V8, etc.) for precise location and replacement instructions. The repair manual will show you the exact steps to remove components like hoses and possibly the intake manifold itself to get to the thermostat.